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Analyzing Prehospital Effects on the Outcome of STEMI Patients

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The research

Ryan D, Craig A, Turner L, et al. Clinical events and treatment in prehospital patients with ST-segment elevation myocardial infarction. Prehosp Emerg Care. 2013;17(2):181–186.

Background: Little is known about clinically important events and advanced care treatment that patients with ST-segment elevation myocardial infarction (STEMI) encounter in the prehospital setting.

Objectives: We sought to determine the proportion of community patients with STEMI who experienced a clinically important event or received advanced care treatment prior to arrival at a designated percutaneous coronary intervention (PCI) laboratory or emergency department (ED).

Methods: We reviewed 487 consecutive community patients with STEMI between May 2008 and June 2009. All patients were geographically within a single, large “third-service” urban EMS system and were transported by paramedics with an advanced care scope of practice. We recorded predefined clinically important events and advanced care treatment that occurred in patients being transported directly to a PCI laboratory or ED (group 1) or interfacility transfer to a PCI laboratory (group 2).

Results: One or more clinically important events occurred in 92 of 342 (26.9%) group 1 patients and nine of 145 (6.2%) group 2 patients. The most common were sinus bradycardia, hypotension and cardiac arrest.

Additionally, 33 of 342 (9.6%) group 1 and nine of 145 (6.2%) group 2 patients received one or more advanced care treatments. The most common were administration of morphine and administration of atropine. Eight group 1 patients and three group 2 patients received cardiopulmonary resuscitation (CPR) or defibrillation.

Conclusions: Clinically important events and advanced care treatment are common in community STEMI patients undergoing prehospital transport or interfacility transfer to a PCI center. Several patients required CPR or defibrillation. Further research is needed to define the clinical experience of STEMI patients during the out-of-hospital phase and the scope of practice required of EMS providers to safely manage these patients.

EMS Science

This month we review a study that sought to determine the frequency of complications suffered by STEMI patients being transported by EMS either directly to a PCI center from the scene or during an interfacility transfer. The Toronto area had only one PCI center in the early part of 2008, but added four more by the end of 2009.

Almost a third of STEMI patients being transported from the scene to a PCI center suffered one or more complications compared to only 7% of interfacility transport STEMI patients. The most common complication was hypotension and bradycardia.

The authors concluded that more research is needed to determine the clinical events surrounding such patients and the appropriate scope of practice of the paramedic caring for them.

Keith Wesley Comments

I applaud the authors for examining what occurs clinically to the prehospital STEMI patient in some detail. The traditional outcomes of time to cath lab have been well-explored and there’s no question that EMS can deliver STEMI patients from the scene to the cath lab faster than if the patient had driven themself.

In this study, the authors compared the clinical events that occurred in prehospital STEMI patients to those who were diagnosed at a non-PCI hospital’s emergency department and were transferred to definitive care.

EMS STEMI patients were three times as likely to suffer a complication compared to the interfacility patient. The decision to bypass a non-PCI facility to stabilize a STEMI patient is a difficult decision. The paramedic is operating under the pressure of the old adage “time is muscle.” Is it worth the increased risk of complication to get the patient to the cath lab?

I would say yes.

But let’s look at this paper more closely. The most common complication was hypotension and bradycardia. I wonder if too-frequent dosing of nitroglycerin caused this? Well over half of all STEMIs are inferior wall infarcts and half of those may involve the right ventricle. Nitroglycerin reduces preload into the right ventricle that can precipitate hypotension.

But why give nitroglycerin at all? Recent studies have found no benefit to nitro in STEMI, and have suggested that it should be reserved for non-STEMI patients. This would eliminate the most common cause of hypotension in the prehospital STEMI patient.

As to the author’s conclusion? I say we don’t need more research on the subject of scope of practice. Instead, we need clarification on the appropriate use of our scope of practice with better guidelines and closer quality review of our performance.

Karen Wesley Comments

Well Doc, I think you missed a key component of this study. The paper shows that interfacility group 2 was found to have significantly fewer adverse events during transport.

The study implies that in comparison, the advanced care given by paramedics in the prehospital setting was suboptimal to that of the ED.

First of all, assessment of cardiac protocols from both the ambulance service and ED would need to be compared. If protocols in the prehospital setting differed from those in the ED, then a revision or update of the prehospital practice might be warranted. However, if both settings used basically the same protocols, the entire ED stay would have to be reviewed to determine the number of adverse events occurring prior to stabilization for interfacility transfer.

My point is that, without evaluation of adverse events in the ED, the study cannot compare the two deliveries of care. Is there evidence to show the patients in the ED setting did not experience any or all of the same events as the prehospital patients?

While I agree with your comment regarding the use of nitroglycerin in STEMI patients, there is nothing in this study to prove that the ED STEMI patients fared better or worse than those cared for by EMS.

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